In order to obtain e.g. white light, light emitted from a LED or a laser diode can be mixed with wavelength converted light emitted from phosphor particles in a phosphor layer having absorbed the emitted light from the LED or laser diode. When light emitted from the LED or laser diode is wavelength converted, heat is generated by the phosphor layer due to Stokes shift and light absorption. When the intensity, or flux density, of the originally emitted light increases, e.g. when it is emitted from a laser diode, the heating power of the phosphor layer also increases.
As can be understood from above, the heating power per area unit of the phosphor layer depends on the area of the phosphor layer. This means that when the area of the phosphor layer is large, the generated heat is more easily dissipated through for example the substrate onto which the phosphor is mounted. On the other hand, when the area of the phosphor layer decreases, this means that the heating power per area unit increases. This may cause the phosphor layer to undergo temperature quenching since all the generated heat cannot dissipate. The effect of temperature quenching is that the emission intensity of the phosphor layer dramatically decreases.
In many embodiments, it is advantageous to reduce the area of the phosphor layer, since the available space for a light emitting device comprising the phosphor layer is small. In JP2009087570 (Sharp KK), such a reduced size is allegedly achieved by e.g. reducing the coupling area between the laser beam and a light guide such that the ratio between the coupling area between the laser beam and a light guide, and the coupling area between the light guide and the phosphor layer is increased. However, since the problem of heat dissipation is not addressed, the phosphor layer cannot be too small or the risk of temperature quenching is increased.
Accordingly, there is a need for an improved way of implementing a light emitting device comprising a phosphor layer, wherein the light emitting device is having improved thermal properties.